The present invention relates generally to time-varying magnetic field detection. More specifically, the present invention relates to systems and corresponding methods for gathering intelligence information based on power frequency, i.e., time-varying, magnetic field measurements and subsequent analysis. The systems and corresponding methods are particularly advantageous for ascertaining the operational status of electrical equipment before and after an event, e.g., a bombing run.
Whenever an electric current flows, a magnetic field is generated. When alternating current, such as that produced by a generator, flows, time-varying magnetic fields of the same frequency are generated and propagate away from the current source. These time-varying magnetic fields travel at the speed of light and can be detected at large distances from the current source. The time-varying magnetic fields generated by transmission and distribution lines may be detected and used to calculate the position, and amplitude of the current source.
As discussed in U.S. Pat. No. 5,525,901, there are a variety of sensors known in the art for use in measuring magnetic fields, such as Hall effect sensors, proton superconducting quantum interference detectors (SQUID), fluxgate magnetometers, inductive pickup sensors, magnetoresistive sensors, and others. For example, Hall effect sensors make use of the property of a current-carrying semiconductor membrane (Hall element) of generating a low voltage perpendicular to the direction of current flow when subjected to a magnetic field normal to its surface. In contrast, magnetoresistive sensors make use of a magnetoresistive effect which is a property of a current-carrying magnetic material to change its resistivity in the presence of an external magnetic field. This change is brought about by rotation of the magnetization relative to the current direction. Depending upon the application, one or another of the above sensors may be chosen for a particular magnetic field measurement. See, also, U.S. Pat. No. 5,777,470, which discloses a compensated coil EMF detector.
U.S. Pat. No. 5,130,655 discloses a multiple-coil magnetic field sensor with series-connected main coils and parallel-connected feedback coils, which is typically employed in subsurface geophysical exploration. In operation, the induced fields generated by an external source penetrate the regions within the coils, and induce voltages proportional to the rate of change of the magnetic field (dB/dt). It is, however, known to provide a direct measurement of magnetic field by use of a feedback coil associated with, and magnetically coupled to, the detector""s main coil. In short, the main coil is coupled to the input terminal of the amplifier, and an output signal is applied to the feedback coil, which coil operates to cancel the magnetic field through the main coil. Thus, the main coil becomes a null detector and the feedback current is linearly proportional to the magnetic field.
Military applications of magnetic field detector systems have generally been confined to applications such as magnetic anomaly detection (MAD) systems, which detect changes in the background magnetic flux associated with large masses of metal. Antisubmarine warfare (ASW) aircraft often trail a MAD sensor, as discussed in U.S. Pat. No. 3,697,869. However, the MAD sensor does not provide the ASW aircraft with any indication of the operational condition of the submarine; additional sensors such as sonabuoys are employed to characterize the condition of the submarine once it has been located.
With the introduction of xe2x80x9cprecision weapons,xe2x80x9d it has become very difficult to perform conventional battle damage assessment, i.e., to determine whether the facility has been physically destroyed, because these precision weapons leave much of the structure intact. For example, when a smart bomb enters a bunker via one of its ventilation shafts, the bunker looks the same in before and after photos. Thus, even when the bunker has been destroyed by the first of several weapons assigned to the bunker, there is no rapid and reliable method by which to determine that the bunker has been neutralized to thereby allow the retargeting of backup weapons to secondary targets. As these precision weapons are further developed, and as the requirements with respect to collateral damage become more stringent, new ways of determining the operating status of equipment are needed.
Another serious problem is to locate and determine the types of operations in hidden (usually underground) facilities. These facilities are often used in the manufacture or storage of weapons of mass destruction. Additionally, locating drug processing laboratories in dense jungle cover is very difficult; these labs are hidden to most sensors (optical, infrared, most RF detectors) by the jungle canopy and the frequently associated cloud cover.
Power frequency magnetic field detection advantageously can be used first to locate and then to monitor the operations in these remote facilities. However, a method and corresponding system for determining the operating condition of a hidden facility based on the time-varying magnetic signature of electrical equipment or electrical power lines supplying that electrical equipment has not previously been proposed.
What is needed is a system and corresponding method for determining and/or inferring the operational condition of a remote facility based on the power frequency magnetic field generated by the remote facility. What is also needed are a system and corresponding method for determining and/or inferring the operational condition of a remote facility based on the power frequency magnetic field generated by the power line(s) supplying electricity to that facility. It would be beneficial if the system and corresponding method could be employed for gathering intelligence regarding the remote facility based on the power frequency magnetic field generated by the remote facility or the power being supplied to that remote facility. It will be appreciated that the intelligence information derived from the system and corresponding methods for determining changes in power frequency magnetic field are not limited to time-varying magnetic fields generated by the fixed remote facility.
It should be mentioned at this juncture that all of the above-identified patents are incorporated herein by reference.
Based on the above and foregoing, it can be appreciated that there presently exists a need in the art for a power frequency, i.e., time-varying, magnetic field (PF-MF) detector and method of operation therefor which overcomes the above-described deficiencies. The present invention was motivated by a desire to overcome the drawbacks and shortcomings of the presently available technology, and thereby fulfill this need in the art.
According to one aspect, the present invention provides a power frequency, i.e., time-varying, magnetic field (PF-MF) detector system for characterizing the operational condition of a remote facility responsive to time-varying magnetic fields generated by electrical transmission lines associated with the remote facility. The PF-MF detector system advantageously includes a PF-MF sensor which generates N time-varying magnetic field data sets, and a PF-MF analyzer which generates an operational condition assessment responsive to the N time-varying magnetic field data sets, wherein N is an integer greater than or equal to 1. Additionally, the PF-MF detector system includes an accumulator, which stores and forwards the N time-varying magnetic field data sets via a communications channel that electrically couples the accumulator to the PF-MF analyzer. In an alternative configuration, the PF-MF detector system includes an accumulator operatively coupled to the PF-MF analyzer, which accumulator stores and forwards the N time-varying magnetic field data sets to the PF-MF analyzer, and a communications channel operatively coupling the PF-MF sensor to the accumulator.
In another aspect, the present invention provides a method for detecting the operational status of electrical equipment disposed at a remote location responsive to power frequency magnetic field (PF-MF) data generated by at least one electrical source providing power to the electrical equipment. Preferably, the method includes steps for obtaining a series of N time-varying magnetic field data sets corresponding to the time-varying magnetic fields generated by the electrical source, and analyzing the N time-varying magnetic field data sets to thereby produce an operational condition to assessment regarding the electrical equipment, where N is an integer greater than or equal to 1.
According to a further aspect, the present invention provides a method for detecting the operational status of electrical equipment disposed at a remote location responsive to power frequency magnetic field (PF-MF) data generated by a PF-MF sensor disposed within the time-varying magnetic field generated by at least one electrical source providing power to the electrical equipment, comprising steps of moving the PF-MF sensor relative to the electrical source, obtaining a series of N time-varying magnetic field data sets corresponding to the time-varying magnetic fields generated by the electrical source, and analyzing the N time-varying magnetic field data sets to thereby produce an operational condition assessment regarding the electrical equipment, where N is an integer greater than or equal to 1.